This invention is generally directed to electrophotographic imaging devices and more specifically to electrophotographic photosensitive devices which in one embodiment are comprised of a layered device containing a specific hole injecting layer and a top layer of an insulating material.
The electrophotographic process, and more specifically the xerographic process is well known. In one known method the latent image present on the photoconductive surface is developed by marking particles such as toner, followed by transfer and fusing of the image to a permanent substrate. Many types of different photoreceptors can be used in such methods including organic materials, inorganic materials and mixtures thereof. There are known photoreceptors wherein the charge carrier generation and charge carrier transport functions are discrete contiguous layers. Also known are photoconductors which include an overcoating layer of an electrically insulating polymeric material and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods.
In the imaging methods using photoreceptors with an overcoating layer as described for example in the text by R. M. Schaffert on Electrophotography published by Focal Press Ltd., London, 1975, it is necessary to store charge carriers at the interface between the photoconductor and the overcoat layer preceeding the imagewise exposure. This is accomplished in non-ambipolar photoconductors by the injection of charge carriers from the substrate electrode into the photoconductor. Thus, in order to obtain a high quality image, the electrode must satisfy the requirements that it injects charge carrier sufficiently and uniformly into the photoconductor. Additionally, the electrode should adhere well to the photoconductor surface and to the supporting base on its back.